Control system for regulating the conductivity of liquids



Jan. 14, 1958 G. RENDEL CONTROL SYSTEM FOR REGULATING THE CONDUCTIVITY LIQUIDS I Filed Nov. 12, 1954 mm) 2 3 T6528 3 A m2] INVENTOR GEORGE H. RENDEL HIS ATTORNEY United States Patent CGNTROL SYSTEM FOR REGULATIN G THE CONDUCTIVITY 0F LIQUIDS George H. Rendel, Pittsburgh, Pa., assignor to United This invention relates to a control system for regulating the conductivity of liquids and more particularly for regulating the conductivity of pickling or cleamng solutions in which a continuous strip passes through the solution in a container or tank. As the strip passes through the tank some of the solution will pass out of the tank on the strip so that the level of the liquid will decrease. The concentration of the solution will decrease as it is used for its intended purpose and in order to obtain best results additional acid must be added to maintain the solution at a given concentration. As the concentration of a solution such as a pickling bath varies the electrical conductivity of the solution will also vary.

It is therefore an object of my invention to providea control system for regulating the conductivity of a liquld in order to maintain the desired concentration of one liquid in another.

Another object is to provide such a control system which maintains the liquid level in a container at a desired level.

Still another object is to provide such a system which will enable the container to be filled with a solution at a predetermined concentration.

These and other objects will be more apparent after referring to the following specification and attached drawing in which the single figure is a schematic diagram showing the control as utilized in a continuous strlp processing line.

Referring more particularly to the drawing, the reference numeral 2 indicates a container or tank for the liquid L. A continuous steel strip S passes over a conductor roll 4 and then downwardly into the tank 2 around slnk rolls 6 and thence from the tank over rolls 8. The strip passes between a pair of electrodes 10 located in the tank 2. The conductor roll 4 and electrodes 10 are connected to a power source 12 which may be a generator excited from a field winding 12F. The power for exciting the field winding 12F may be supplied from a suitable direct current power source 14 through a rheostat 16 connected in series with the field winding 12F to control the amplitude of excitation applied to generator 12. Water is supplied to the tank 2 through a conduit 18. An acid or other electrolyte is delivered to the tank 2 from a reservoir 20 through a conduit 22. The apparatus so far described is conventional. A conductivity cell 24 is provided in tank 2 below the normal level of the liquid L. The conductivity cell 24 has two electrodes 26 connected to a constant potential A. C. power source 28. An ad ustable potentiometer 30 is provided in one of the leads between the electrodes 26 and power source 23. Adjustabie arm 32 of the potentiometer 30 is connected to the grid 34G of an electronic tube 34 by means of lead wire 36. The tube 34 also has a cathode 34C and plate 34F. The cathode 34C is connected to one side of the potentiometer 35) through wire 38. A battery 40 is connected across the wires 36 and 38 and provides a bias potential for the tube 34. Tube 34 is also part of a circuit including a relay coil 42 and a suitable power source such as a 2,819,726 Patented Jan. 14, 1958 battery 44. The relay coil 42 is provided with contacts 42C. A valve 46 in the conduit 22 is operable by means of a solenoid 48. Power for operating solenoid 48 is provided by means of a circuit including power line L1, lead 50, contacts 42C, contact 520 and power line L2. Contact 520 is part of a standard cycle timer 52 which includes a motor 54 connected to drive a cam 56 and a cam follower 58 connected to control the operation of contact 52C. The cycle timer is such that the contact 520 will be closed for a predetermined time interval and will then open for the remaining time of each revolution of the cam 56. The motor 54 is energized from the lines L1 and L2 when a contact 600 operable by a relay coil 60 is closed. Energization of the relay coil 60 is controlled by line control 62 and the coil 60 will be energized when the processing line is operating. Solenoid 48 is also energized when contact 64C is closed, this contact 64C being connected in parallel with contact 52C. Contact 64C is part of a conventional timing relay 66 having a motor 68 mechanically connected to a cam 70 and a cam follower 72 connected to operate contact 64C. This conventional timing relay is such that its contact 64C will close when motor 68 is energized and will open after a predetermined time period and will then remain open as long as motor 68 remains energized. Motor 68 becomes energized when contact 74C of a double pole switch is manually closed. A valve 76 operable by solenoid 78 is provided in conduit 18. Solenoid 78 is connected to spaced probes 80 and is energized from the secondary 828 of a transformer 82 which is connected to power source L1L2 through contact 74C1 of the double pole switch. The probes 80 may be located in tank 2 but are preferably located in a tank 84 connected to tank 2 through conduit 86. The bottom of probes 80 is located at the desired level of the liquid in the tank 2. A second pair of probes 88F and 88P1 are also located in the tank 84 with the probe 88F being at the desired minimum level of the liquid in the tank 2. Probes 88F and 88P1 are connected to the secondary 828 in series with a relay coil 98. Relay coil 98 is provided with contacts 90C and contacts 90C1. Contacts 90C are connected in circuit with line control 62 through a push button switch 92. Contacts 90C1 complete a circuit from the lines L1 and L2 through a light or other signal device 94.

The operation of my device is as follows:

Assuming that there is no liquid in the tank 2 and that it is desired to fill the tank with an electrolyte consisting of about water and 5% sulphuric acid by weight and to maintain this concentration, the contact arm 32 of potentiometer 30 is adjusted to maintain this concentration. The double pole switch having contacts 74C and '74C1 is closed. Since the probes 80 are out of the liquid the circuit through solenoid 78 will remain open and the valve 76 will also be open so that water is delivered to the tank 2 through conduit 18. The processing line is stopped so that contact 52C will be open. However, timing relay motor 68 will be energized thus closing contacts 64C and completing a circuit to solenoid 48 which opens valve 46 and permits acid to flow from reservoir 20 through conduit 22 into tank 2. The timing relay 66 is set so that the solenoid 48 will be energized and valve 46 opened for a sufiicien't length of time to permit the desired amount of acid to flow into the tank 2. After this predetermined time is over contacts 64 will open and remain open as long as motor 68 is energized. Because the line is not operating during the filling of the tank 2 contact 60C is open so that the concentration control system is inactivated. After the acid flow stops water will continue to flow until it reaches probes 80 when a circuit will be completed through solenoid 78 to close valve 76. The push button switch 92 is then closed and.

the line started in operation thus energizing coil 60 and closing contacts 60C. This energizes motor 54 and starts the cycle timer 52 in operation. The cycle timer 52 is preferably setso that its contacts will be closed only for a relatively short time for each revolution of the cam 56. For a typical operating condition this relay may be adjusted so that the contacts 520 will close for about 30 seconds during each five minute period of operation. Since the output potential from power source 28 is substantially constant the current that flows between electrodes 26 will be approximately proportional to the electrical conductivity of the electrolyte. The potential drop across the terminals of potentiometer 30 is proportional in amplitude to the current conducted between electrodes 26. The voltage drop across potentiometer 30 provides an electrical signalto actuate the conductivity control system. When the electrolyte in tank 2 is at the desired concentration the current that flows between the electrodes 26 is adequate to cause a potential drop between movable contact arm 32 and wire 38 of a value about equal in amplitude to the potential from battery 40. Under these con ditions grid 346 is slightly positive with respect to cathode 34C and therefore tube 34 willconduct current, thus energizing control relay coil 42. This opens contacts 42C so that there will be no current flowing in solenoid 48 and the valve 46 will remain closed. As the concentration of the acid in the tank 2 decreases the conductivity of the electrolyte also decreases and the current flow between electrodes 26 decreases. Therefore the potential between movable contact arm 32 and line 38 diminishes. When this potential is reduced to a value less than that of battery 40 the battery potential predominates and the grid 346 will prevent tube 34 from conducting. This deenergizes relay coil 42 causing its contacts 42C to close. When contacts 42C close solenoid 48 will be energized during the time that contacts 52C are closed and acid will flow from reservoir into the tank 2 for a period of seconds. The acid will then have 4% minutes to disperse through the tank and if the conductivity still remains below that desired the solenoid 48 will again be energized for a period of 30 seconds. Thus acid will be continuously added for one half minute out of every five minutes until the conductivity reaches the desired value after which contacts 42C will open, thus discontinuing the flow of acid. When the liquid level falls below the bottom of probes 80 solenoid 78 will be deenergized and valve 76 will open thus causing flow of Water into the tank 2 until the liquid level reaches the bottom of probes 80. When the liquid level falls below the probe 881 relay coil 90 will be deenergized thus opening contacts 90C and closing contacts 90C1. Closing of contacts 90C1 completes a circuit to light 94 thus warning the operators that the liquid level is low and that something is wrong with the controls. Opening of contacts 90C interrupts the circuit to the line control thus stopping the processing line.

While one embodiment of my invention has been shown and described it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. In apparatus including a container for a liquid mixture containing Water and a substance which changes the conductivity of the mixture in accordance with the amount of said substance in the mixture, a first conduit for supplying said substance to said container and a second conduit for supplying water to said container; a control system for filling the container and regulating the conductivity of the liquid comprising a conductivity cell in said container, an electric circuit for supplying electric current to said cell, a potentiometer in said circuit, an electronic tube having a grid and cathode connected across said potentiometer, means for supplying a bias voltage to said tube in opposition to the voltage from said potentiometer, a second electric circuit including said tube, a power source and a relay coil, a third electric circuit including a contact and a solenoid connected in series, said contact being connected for operation by said relay coil, a second contact connected in parallel with the first contact, a timing relay connected to operate said second contact, and a valve in said first conduit controlled by said solenoid.

2. In apparatus including a container for a liquid mixture containing water and a substance which changes the conductivity of the mixture in accordance with the amount of said substance in the mixture, a first conduit for supplying said substance to said mixture and a second conduit for supplying water to said container; a control system for filling the container and regulating the conductivity of the liquid comprising a conductivity cell in said container, an electric circuit for supplying electric current to said cell, a potentiometer in said circuit, an electronic tube having a grid and cathode connected across said potentiometer, means for supplying a bias voltage to said tube in opposition to the voltage from said potentiometer, a second electric circuit including said tube, a power source and a relay coil, a third electric circuit including a first contact, a second contact and a solenoid connected in series, said first contact being connected for operation by said relay coil, a valve in said first conduit controlled by said solenoid, a cycle timer connected to operate said second contact, a third contact connected in parallel with the first and second contacts, and a timing relay connected to operate said third contact.

3. In continuous strip processing lines including a container for a liquid mixture containing water and a substance which changes the conductivity of the mixture in accordance with the amount of said substance in the mixture, a first conduit for supplying said substance to said mixture and a second conduit for supplying water to said container, and means for controlling the movement of strip through the container; a control system for filling the container and regulating the conductivity of the liquid comprising a conductivity cell in said container, an electric circuit for supplying electric current to said cell, a potentiometer in said circuit, an electronic tube having a grid and cathode connected across said potentiometer, means for supplying a bias voltage to said tube in opposition to the voltage from said potentiometer, a second electric circuit including said tube, a power source and a relay coil, a third electric circuit including a first contact, a second contact and a solenoid connected in series, said first contact being connected for operation by said relay coil, a valve in said first conduit controlled by said solenoid, a cycle timer connected to operate said second contact, a third contact connected in parallel with the first and second contacts, a timing relay connected to operate said third contact, a valve in said second conduit, means responsive to the level of liquid in said container for controlling the operation of said last named valve, and means for activating said last named means prior to the activation of the said electric circuits.

References (liter! in the file of this patent UNITED STATES PATENTS 1,319,734 Thorold Oct. 28, 1919 1,558,060 Stead Oct. 20, 1925 2,176,471 Pyle Oct. 17, 1939 2,377,363 Noble et a1 June 5, 1945 2,492,174 Noble Dec. 27, 1949 2,560,854 Ferrand July 17, 1951 2,586,169 Kline Feb. 19, 1952 2,593,825 Albrecht Apr. 22, 1952 

